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    Subject[PATCH 3.18 14/19] scsi: sg: recheck MMAP_IO request length with lock held
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Todd Poynor <toddpoynor@google.com>

    commit 8d26f491116feaa0b16de370b6a7ba40a40fa0b4 upstream.

    Commit 1bc0eb044615 ("scsi: sg: protect accesses to 'reserved' page
    array") adds needed concurrency protection for the "reserve" buffer.
    Some checks that are initially made outside the lock are replicated once
    the lock is taken to ensure the checks and resulting decisions are made
    using consistent state.

    The check that a request with flag SG_FLAG_MMAP_IO set fits in the
    reserve buffer also needs to be performed again under the lock to ensure
    the reserve buffer length compared against matches the value in effect
    when the request is linked to the reserve buffer. An -ENOMEM should be
    returned in this case, instead of switching over to an indirect buffer
    as for non-MMAP_IO requests.

    Signed-off-by: Todd Poynor <toddpoynor@google.com>
    Acked-by: Douglas Gilbert <dgilbert@interlog.com>
    Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/scsi/sg.c | 7 +++++--
    1 file changed, 5 insertions(+), 2 deletions(-)

    --- a/drivers/scsi/sg.c
    +++ b/drivers/scsi/sg.c
    @@ -1798,9 +1798,12 @@ sg_start_req(Sg_request *srp, unsigned c
    !sfp->res_in_use) {
    sfp->res_in_use = 1;
    sg_link_reserve(sfp, srp, dxfer_len);
    - } else if ((hp->flags & SG_FLAG_MMAP_IO) && sfp->res_in_use) {
    + } else if (hp->flags & SG_FLAG_MMAP_IO) {
    + res = -EBUSY; /* sfp->res_in_use == 1 */
    + if (dxfer_len > rsv_schp->bufflen)
    + res = -ENOMEM;
    mutex_unlock(&sfp->f_mutex);
    - return -EBUSY;
    + return res;
    } else {
    res = sg_build_indirect(req_schp, sfp, dxfer_len);
    if (res) {

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